1. Field of the Invention
This invention relates to cameras with exposure control systems, and more particularly to a camera capable of making exposure with the shutter time value and aperture value related to each other in a predetermined combinational scheme, or so-called program mode, and in shutter preselection automatic mode.
2. Description of the Prior Art
It is already known to provide a program automatic exposure control system having a predetermined scheme of combinations of shutter time values (Tv values) and aperture values (Av values) illustrated by a functional line B (program curve) in FIG. 1, one of which combination is selected according to the brightness of reflected light from an object being photographed (Bv value) to derive an effective exposure value (Ev value).
In such conventional program shutter camera, after the object brightness is measured, the film speed value (hereinafter called Sv) and the object brightness value (hereinafter called Bv) are computed to derive the exposure value (hereinafter called Ev) in the form of a combination of a shutter speed value (hereinafter called Tv) and an aperture value (hereinafter called Av). For example, when Ev=10, as the program curve B illustrated is operative, it is found that Tv=1/4 (sec.) and Av=16 (F-number). Since at this time these Av and Tv values are unequivocally determined on the basis of Ev, the photographer is unable to freely select either Tv or Av. That is, Tv and Av take values by themselves based on the brightness. Because of this, the conventional program automatic exposure control system has a problem that in low lighting situations, the shutter time is adjusted to a longer value than that at which shaking of the hand occurring when actuating the shutter button becomes noticeable.
Attempts have been made to readjust the shutter time, which is obtained by the program curve (for example, B in FIG. 1) when the brightness is lowered, to a somewhat shorter value by shifting the program curve B along a dot-and-dash line A to lie at L.sub.0 and in some cases, further changing the angle of inclination, .alpha., of the new program curve L.sub.0 with the resultant program curve indicated at C'.
Even such approach is, however, found to lead to an unacceptable possibility of the occurrence of longer shutter times than the limit due to shaking of the hand as it often happens that the brightness is further lowered, thus failing to eliminate the problem of shaking this hand.